Networking Question

[slinga]

I'm looking for a way to get all machines in a single collision domain (i.e. hub, wireless network) to respond to a "hello" packet, regardless of ip address\subnet mask.

I was thinking about sending a ping packet like this:

Destination IP: 255.255.255.255 (not sure about this)

Destination Mac: FF-FF-FF-FF

Something like that. Don't have any test machines to try this on, but what do you guys think?

 

[Curtis]

If you just want to ping the broacast domain, then you'll need a differnt address. If your local network address is 192.168.1.0, then the broadcast address is 192.168.1.255. I tried a broadcast ping on an XP box and a linux box, but in both cases only one device responded - curiously my WLAN access point.

 

[slinga]

I'm not really looking for all the machines in the subnet.

I want all the machines in the collision domain which is a subset of all the machines in the subnet. The problem with pinging the subnet broadcast is I won't know the ip addresses of the other nodes on the network. Pretty much all ad-hoc stuff I think.

Edit: I should clarify a bit, the machines connected together won't necessarily have the right (as in correct subnet) ip addresses or any ip address information for that matter.

 

[Curtis]

Well the 255.255.255.255 address does not work under XP. Under Linux, again it only returned one address, this time the address of my DSL modem (it resides on another network, 192.168.0.0).

EDIT: Hang on, a "colision domain" isn't something that a network is actively aware of. It has no reference or understanding of what a colision domain might be. If you're subnetting, then each subnet knows about the computers on that subnet. Unless there is a router (or layer 3 switching device) on the network, subnets cannot talk to other subnets.

 

[ExCyber]

If I'm understanding the way ARP works correctly, I think your scheme should work if you can actually force the Ethernet address to FF-FF-FF-FF-FF-FF

edit: it occurs to me that it's highly likely that just pinging 255.255.255.255 with a TTL of 1 will get pretty close, but will still go through switches and the like, which isn't strictly the same collision domain.